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Asked: 2026-06-09T19:14:16+00:00

I’ve got a sql output into a data.frame which looks like this: dateTime resultMean

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I’ve got a sql output into a data.frame which looks like this:

  dateTime              resultMean           SensorDescription
1 2009-01-09 21:35:00   7.134589             Aanderaa Optode - Type 3835
2 2009-01-09 21:35:00   7.813000         Seabird SBE45 Thermosalinograph
3 2009-01-09 21:35:00   8.080399 Turner SCUFA II Chlorophyll Fluorometer
4 2009-01-09 21:35:00   7.818604                          ADAM PT100 PRT
5 2009-01-09 21:36:00   7.818604                          ADAM PT100 PRT

I want to turn it into a frame like so:

  dateTime              Aanderaa Optode - Type 3835  Seabird SBE45 Thermosalinograph   Turner SCUFA II Chlorophyll Fluorometer   ADAM PT100 PRT               
1 2009-01-09 21:35:00   7.134589                     7.813000                          8.080399                                  7.818604

Currently I’ve got a function which splits by SensorDescription, then loops over the list with merge.
Is there a better way of doing this using built in functions? I’ve looked at plyr, ddply etc and nothing seams to do quite what I want.

the current merging loop functions looks like this:

    listmerge = function(datalist){
    mdat = datalist[[1]][1:2]
    for(i in 2:length(datalist)){
        mdat = join(mdat,datalist[[i]][1:2], by="dateTime", match = "all")
    }
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1 Answer

  1. Editorial Team

    You can use dcast from the reshape2 package:

    d <- data.frame(x=1, y=letters[1:10], z=runif(10))
dcast(x ~ y, data=d)
Using z as value column: use value.var to override.
  x         a         b         c         d         e         f         g         h        i        j
1 1 0.7582016 0.4000201 0.5712599 0.9851774 0.9971331 0.2955978 0.9895403 0.6114973 0.323996 0.785073

    reshape from the base stats package can also accomplish this, but the syntax is a little more difficult.

    reshape(d, idvar='x', timevar='y', direction='wide')

  x       z.a       z.b       z.c       z.d       z.e       z.f       z.g       z.h      z.i      z.j
1 1 0.7582016 0.4000201 0.5712599 0.9851774 0.9971331 0.2955978 0.9895403 0.6114973 0.323996 0.785073
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